1. Field of the Invention
The present invention relates to a wireless communication device and a wireless communication method.
2. Description of the Related Art
With improvement of the communication speed and the usability, wireless communication techniques have been used widely in various situations and locations, for example, in the houses, offices, and schools. Wireless communication devices have been proposed to have various functions including broadband router function as well as general access point function.
One of such functions is WDS (wireless distribution system) that establishes wireless data communication between at least two LANs. The WDS may be actualized by data transmission between access points included in respective wireless LANs or by an exclusive repeater device. In either way, the WDS technique assures data transmission to and from entities registered in advance and expands the physical coverage or the device coverage of wireless communication, thus enhancing the convenience of wireless communication. Such relaying function for the wireless LANs is described in, for example, Japanese Patent Laid-Open No. 2003-249937.
With advance of the wireless communication technology, there is a movement to extend the available range of carrier waves for wireless communication. This movement gives permission for the use of a 5 GHz frequency band, in addition to the conventionally used 2.4 GHz frequency band. In Japan, a frequency band of 5.25 to 5.35 GHz (corresponding to a W53 frequency band with four channels 52/56/60/64) was permitted for the indoor application in 2005. A W56 frequency band (5.4700˜5.725 GHz) with eleven channels 100/104/108/112/116/120/124/128/132/136/140 was permitted for both the indoor application and the outdoor application in 2007.
The W53 and W56 frequency bands are generally used by various radars including moving radars, such as radars on boats and ships, aircraft radars, and radars for military purposes and stationary radars, such as weather radars. There is accordingly a possibility of interference with radio signals used by such equipment. For the purpose of adequate assignment, the wireless communication devices are obliged to avoid interference by DFS (dynamic frequency selection) technique. The DFS requirement monitors each channel for one minute prior to an actual use of the channel and gives permission for starting the actual use of the channel only after confirmation of no detection of radar/radio signals at the channel. The DFS requirement also monitors detection of radar/radio signals at a currently used channel and, in the event of detection of radar/radio signals, takes an adequate interference-avoiding operation, such as a prompt stop of the use of the channel within 10 seconds. Avoiding the interference by DFS is required in the countries such as China and Europe in which the use of the W53 or W56 frequency band is permitted.
In the state where a wireless communication device is used as a repeater device for interconnecting different wireless LANs, in response to detection of radar/radio signals at a currently used channel, the wireless communication device immediately stops the use of the currently used channel but can not reestablish communication at a newly allocated channel within a short time period. The wireless communication device is not informed of which channel is selected by the other end of communication and is thus required to successively perform scans at all available channels in order to identify the channel selected by the other end of communication.